The intermittent nature of energy supplied by photovoltaic and wind electricity generation has increased the need for energy storage that allows energy to be stored and retrieved on demand. Batteries provide a convenient mode of energy storage that can be located close to the site of generation. However, batteries can suffer disadvantages associated with their high cost, temperature sensitivity, and insufficient service or cycle life. In addition, as batteries are scaled up to meet the energy storage demands of medium scale applications of tens to hundreds of kilowatt hours there are concerns about the safety of these systems, particularly when the negative electrode incorporates lithium ion technology. Aqueous flow batteries have been developed as a possible solution to the large scale storage of energy. By using active material stored external to the electrode stack they have been proposed as a low cost and readily scalable solution to large scale energy storage. The physical separation of active materials in so called flow type batteries is also a significant factor in improving the safety of the systems for use in a home environment. However, some of these batteries have used toxic halogen materials while other systems have used expensive transition metals such as vanadium or chromium. In general, the costs and the system lifetimes have not met expectations. This is particularly true in kilo Watt hour scale systems that must maintain high performance, even as the increased size of the system dictates more complex electrochemical engineering solutions. In this specific application there is also a need for higher volumetric energy density than is normally associated with medium sized redox flow batteries. In efforts to control costs there has been a recent emphasis on organic redox couples in aqueous media that have the potential for high cycle life and low cost. However, the solubility limitations and relatively low voltages are significant drawbacks to the viability of the systems.